Hello there! Yes. 21/48 would have to be simplified to get a simpler fraction. Keep in mind that whatever you do to the numerator, you must do to the denominator. If you write out the factors for each of the number, you see that they both have a factor of 3. We can divide both sides by 3 to get 7/16. We can't divide that fraction anymore, so 7/16 is a fraction in simplest form.